The present invention relates to an apparatus for analyzing composition, structure, an electronic condition and the like of a sample by measuring the energy and direction distribution of the movement of charged particles emitted from the sample, and more particularly to an apparatus for analyzing energy distribution of charged particles emitted from a sample or two-dimensional direction distribution of charged particles having specific energy.
FIG. 3 shows an analyzer proposed by Eastman et al. The analyzer is characterized by comprizing a low-pass filter composed of a ellipsoidal mirror M and a grid G3 and a high-pass filter composed of spherical grids G4 and G5 being concentric. A sample S is positioned at one of the focuses of the ellipsoidal mirror M. A small opening A is arranged at the other of the focuses of the ellipsoidal mirror M. A two-dimensional detector D is provided at the outside of the grids G4 and G5.
In the above-stated apparatus, in principle, the number of the grids G3, G4, and G5 is three. Actually, additional accelerating grids G5 and G6 are needed to accelerate the charged particles to operate the two-dimensional detector D. An additional grid G7 is needed for the charged particles to travel straight between the grid G6 and the detector D. Further, two additional grids G1 and G2 being concentric and double-sphere are provided around the sample S. Totally, eight grids are needed. Fundamentally, the image of the direction distribution of the charged particles is distorted. Regarding an orbit b and another orbic c of the charged particle with an angle .theta. around an orbit a of the charged particles emitted from the same S, when the direction of the orbits b and c is somewhat changed, the direction at the opening A is changed in which the direction change of the orbit b is reduced and that of the orbit c is magnified. To amend this distortion, the plane of the detecter D is rotated clockwise about an axis perpendicular to the drawing in FIG. 3. In order to amend the distortion in this manner, the value of the angle .theta. is not much. Further, the image on the detector D of the charged particles emitted along a circular cone having a vertical angle of 2 .theta. around the orbit a is not circular. As a still further fundamental fault, in connection with the orbit of electrons unlike that of light, the ellipsoidal mirror is provided in which an imaginary reflection supposed on the base of the orbits of electrons does not correctly equal the plane of the ellipsoidal mirror. This discrepancy becomes much as a solid angle is greater, so that it becomes difficult to converge the electrons. Therefore, a great solid angle cannot be measured.
Moreover, it is difficult to make the ellipsoidal mirror M. When the ellipsoidal mirror M is replaced by a spheroid mirror, the charged particles cannot gather precisely at the position of the opening A if the distance between the sample S and the opening A is short as compared to the diameter of the spherical mirror. However, as the orbits of the charged particles are far from the central orbit a, an aberration becomes remarkable. On account of limiting the aberration, the solid angle to be measured is further reduced.